Antichatter positive feed control for broaching machines and the like



Feb. 10, 1970 R. A. LENTZ ETA!- 3,

ANTICHATTER POSITIVE FEED CONTROL FOR BROACHING MACHINES AND THE LIKE Original Filed June 2, 1967 .4 Sheets-Sheet 1 NEUTRAL INVENTORS REX A. LENTZ a SYLVESTER RCUDNOHUFSKY R. A. LENTZ ET AL ANTICHATTER POSITIVE FEED CONTROL FOR Feb. 10, 1970 BROACHING MACHINES AND THE LIKE Original Filed June 2, 1967 .4 Sheets-Sheet 2 INVENTORS REX A. LENTZ a SBYWESTER R. CUDNOHUFSKY ATTORNEY mxOmFw mmBOa Feb. 10, 1970 R. A. EENTZ E AL ANTICHATTER POSITIVE FEED CONTROL FOR BROACHING MACHINES AND THE LIKE Original Filed June 2, 1967 .4 Sheets-Sheet S filllll... W 5 Y m u E TU M N W U G R X F ER RE T s w L Yv B SOL HYD mxOmhm ZED-rum R. A. LENTZ L. ANTICHATTER POSITIVE FEED CONTROL FOR Feb. 10, 1970 BROACHING MACHINES AND THE LIKE Original Filed June 2, 1967 I .4 Sheets-Sheet 4 INVENTORS REX A. LENTZ 8( SBY}I VESTER. R. CUDNOHUFSKY ATTORNEY United States Patent Int. Cl. F15!) 15/18 US. Cl. 60-52 7 Claims ABSTRACT OF THE DISCLOSURE An antichatter positive feed control for broaching machines and the like wherein a tool or work carrying slide is hydraulically advanced to perform heavy work loads and retracted to its start position by a hydraulic power cylinder generally of a size requiring a relatively high volume of oil for each power and return stroke employing a variable displacement pressure compensated or manually adjustable motor driven main pump to provide the required volume of oil under the required pressure to the inlet end of power cylinder during its power stroke while oil is simultaneously being forced out of or expelled from the outlet end of the power cylinder through a positive displacement or metering pump preferably driven by the same motor that drives the variable displacement pressure compensated pump. The said meterin g pump meters the oil expelled from the power cylinder, thus providing a positive feed control of the tool or work carrying slide regardless of varying or intermittent cutting loads encountered by the said slide, the hydraulic system further preferably including automatic means for bleeding air from the hydraulic system and for maintaining the power cylinder filled with oil when the machine is at neutral between the return and power strokes of the power cylinder.

This application is a continuation of Ser. No. 643,192 filed June 2, 1967, now abandoned.

Heretofore, the conventional methods of driving the tool or work slide or ram of a hydraulic broaching machine or the like generally consists of the employment of a power cylinder having its piston connected to the tool or work slide. On its power stroke, oil under suitable pressure and volume is directed into the power cylinder at its inlet and against the piston thereof from a valve, piston or screw type pump. Movement of the piston during its power stroke forces oil out of the outlet end of the cylinder through a relief or back pressure valve set to maintain a suitable selected operating pressure against the piston head during the power stroke of the piston whereby to provide smooth piston action with a resultant smooth advance of the tool or work slide. When the selected operating pressure is reached, the relief valve opens and releases oil from said outlet end of the cylinder for return to the oil tank. Such prior conventional systems for driving a tool slide or work slide do not assure smooth advancement of the tool or work slide during the power stroke because at pressures above the pressure setting of the back pressure relief valve less than the optimum desirable control of advancement of the tool or work slide is obtainable which results in tool chatter, intermittent vibration or uncontrolled oscillation of the tool or work slide with resultant poorly finished broach cuts in the workpiece.

With the foregoing in view, the primary object of the instant invention is to provide an antichatter positive feed control means for broaching and like machines having a tool or work carrying slide or ram wherein tool chatter or intermittent work vibration or uncontrolled oscillation is substantially eliminated for all practical purposes.

Another object of the invention is to provide an antichatter positive feed control means for the slide or ram of broaching machines or the like wherein a variable displacement pump with pressure compensation provides the required volume and pressure of oil to the inlet end of a cylinder during its entire power stroke while oil in the outlet end of the cylinder is simultaneously expelled through a positive displacement flow control metering pump whereby to provide a positive feed control of the slide or ram throughout its entire power stroke.

A further object of the invention is to provide in an antichatter feed control means as set forth above including means for bleeding air from the hydraulic system and maintaining the power cylinder filled with oil on the discharge side of the piston when the machine is at neutral between the return and power stroke of the slide or ram.

Other objects of the invention will become apparent by reference to the following description taken in connection with the accompanying drawing, in which:

FIG. 1 is a diagrammatic view of an antichatter feed control circuit of the invention as applied to the hydraulic system of a single slide pull-down type broaching machine, the control circuit preferably being of the regenerative type to accomplish rapid return of the broaching slide FIG. 1A is a fragmentary sectional view through the power cylinder showing the preferred location of an automatic air bleeder employed to bleed air from the hydraucic system and the power cylinder that tends to accumulate therein.

FIG. 2 is a diagrammatic view similar to FIG. 1 showing the control circuit during the Power Stroke of the piston.

FIG. 3 is a diagrammatic view similar to FIGS. 1 and 2 showing the control circuit during its Return Stroke of the piston FIG. 4 is a diagrammatic view of an antichatter feed control circuit of the invention similar to the feed control circuit of the invention disclosed in FIG. 1 except that it has been applied to the hydraulic system of a single slide push-down type broaching machine with the regenerative feature omitted.

FIG. 4A is a sectional view showing the preferred location of an automatic air bleeder employed in the embodiment of the invention disclosed in FIG. 4 to bleed air from the hydraulic system and the power cylinder that tends to accumulate therein.

Disclosed diagrammatically in FIGS. 1, 1A, 2 and 3 is an illustrative embodiment of an antichatter positive feed control of the invention applied to drive the tool slide 10 of a pull-down broaching machine by means of its power cylinder 11 having a piston 12 therein connected by the piston rod 13 extending from the piston 12 of said power cylinder 11 to the tool slide 10, the hydraulic circuit of which is shown at Neutral in FIG. 1, at Power Stroke in FIG. 2, and at Return Stroke in FIG. 3. For the purpose of the description of the invention, the inlet and outlet ends of the power cylinder 11 are at the upper and lower ends respectively thereof as viewed throughout the drawings.

A variable displacement pressure compensated or manually adjustable main pump 20 provides an adequate volume of oil at a selected pressure substantially greater than required for the heaviest broaching cut preferably manually set by controls on the pump. The said main pump 20 furnishes oil under pressure from a hydraulic fluid reservoir tank T to the inlet end of the power cylinder 11, which pump 20 is preferably driven by one end shaft of a double end shaft motor 21. A positive displacement metering pump 22 driven by the other end shaft of the double end shaft motor 21 meters oil expelled from the outlet end of the power cylinder 11 to the tank T at a manually preset rate providing a corresponding selected positive feed rate of movement of the power stroke of the broach slide 10. Obviously, the positive displacement metering pump 22 may be set responsive to suitable servo means (not shown) to provide selected variations in the rate at which oil is expelled from the outlet end of the power cylinder 11 whereby to provide corresponding variations in the feed rate of movement of the tool slide 10.

A solenoid controlled pilot operated '4-way hydraulic circuit 4-way control valve 25 is preferably used to sequentially establish the Neutral, Power Stroke and Return Stroke conditions of the hydraulic circuit employed to move the tool slide of a broaching machine from Neutral through its Power and Return Strokes back to Neutral. The said 4-way control valve 25 is preferably spring loaded to its Neutral position, is hydraulically shifted responsive to the actuation of Solenoid PS to its Power Stroke position, is hydraulically shifted responsive to the actuation of Solenoid RS to its Return Stroke, and is hydraulically shifted responsive to the deactuation of either of the Solenoids PS or RS to its spring loaded Neutral position. The electric circuits actuating the Solenoids PS and RS are not diagrammed inasmuch as any conventional electric circuit may be employed which could be manually or otherwise operated as may be required or desired in any particular installation.

Referring now particularly to FIGS. 1 and 1A, the broaching slide 10 is in its UP or returned position, the 4-way control valve 25 is in its central or Neutral position, and the motor 21 is running and driving the main pump 20 and the metering pump 22. Hydraulic fluid under pressure is supplied from the tank T by the main pump 20 to the pilot hydraulic system (not shown) of the 4-way control valve through the line 30. Hydraulic fluid under pressure is also supplied by the main pump 20 to the outlet end of the power cylinder 11 through the line 30, a relatively small by-pass line 31, and a portion of the line 32. A manually set flow control valve 33 is provided in the by-pass line 31 to regulate the volume of hydraulic fluid passing therethrough into the outlet end of the power cylinder 11. The upper portion of the power cylinder 11 just below the lower piston ring 120 of the piston 12 thereof is preferably provided with an air bleed outlet 34 through which air is bled together with hydraulic fluid passing from the power cylinder 11 below the said piston 12 into the line 35, through the 4-way control valve 25 and the line 36 to and through the metering pump 22 to the hydraulic fluid tank T.

From the foregoing, it will be observed that when the broaching slide 10 is in its UP or returned position and the 4-way control valve 25 is in its Neutral position, any air that may enter or may have accumulated in the main hydraulic system and the power cylinder during the previous Power and Return Stroke of the broaching slide is beld and expelled therefrom.

The said air bleed also functions to maintain the piston 12 and the broaching slide 10 in their UP or returned position responsive to hydraulic fluid under pressure applied to the piston 12 from the main pump 20 when the said 4-way control valve 25 is in its Neutral position.

It will be noted that whenever the positive displacement metering pump 22 is not receiving sufiicient hydraulic fluid from the power cylinder 11 to permit it to function as required on the Power Stroke of the piston 12 thereof, hydraulic fluid is supplied thereto through a line 37 from the tank T which is connected to the line 36 on the inlet side of the said metering pump 22. A suitable spring loaded closed check valve 38 is provided in the line 37 to prevent flow of hydraulic fluid from the tank T to the metering pump 22 when hydraulic fluid is being forced under pressure from the cylinder 11 to the metering pump 22.

In FIG. 2, the Solenoid PS has been actuated usually by a push button type START switch (not shown) which initiates a Broaching Cycle by causing the hydraulic operated 4-way control valve 25 to shift to the left as viewed in the drawings whereupon the Power Stroke of the broaching slide is initiated. During the said Power Stroke, hydraulic fluid under the required volume and pressure is supplied by the main pump 20 to the inlet end of the power cylinder 11 through the line 30, the 4-way valve 25 and the line 35 which moves the piston 12 of the power cylinder 11 and broach slide it on their Power Stroke. During said Power Stroke, hydraulic fluid is returned from the outlet end of the power cylinder 11 through the line 32, the 4-way valve 25, and the line 36 to and through the metering pump 22 to the tank T.

The positive displacement or metering pump 22 is preferably of the piston type including a volume control which may be manually operated or servo operated as desired or required to provide control of the speed of the broaching slide 10 or whatever other hydraulically powered machine element that may be driven on the power stroke of the piston 12 of the power cylinder 11. In a broaching machine or the like wherein the work done by the piston 12 varies during the power stroke of the piston due to variations in the broach cut on work being broached, as the case may be in many broaching or other machine operations where tool chattering or work vibration is likely to occur, a feed control of the invention is of extreme value in providing a selected rate of movement of the power stroke of the piston 12 with the rate of cut of a broach or the like remaining constant or at a pre-selected rate regardless of varying and intermittent load requirements during any complete power stroke of the piston 12. Although not shown, it is obvious that by servo operated control of the metering pump 22, the speed of the broaching slide 10 or any other hydraulically powered machine element may be varied during the course of any power stroke thereof.

In FIG. 3, the Solenoid RS has been actuated by such means as the closing of a limit switch (not shown) which is contacted by the broaching slide at the end of the Power Stroke thereof which causes the 4-way control valve 25 to shift to the right as viewed in the drawings whereupon the Return Stroke of the broaching slide is initiated. To provide a rapid return of the broaching slide 10 on its Return Stroke, a regenerative hydraulic circuit described below is preferably employed.

During the said Return Stroke, hydraulic fluid under the required volume and pressure is supplied by the main pump 20 to the outlet end of the power cylinder 11 through the line 30, the 4-way valve 25 and the line 32 which moves the piston 12 of the power cylinder 11 and broach slide 10 on their Return Stroke. During the said application of hydraulic fluid under pressure from the main pump 20 to the outlet end of the power cylinder 11, hydraulic fluid is forced out of the inlet end of the power cylinder 11 through the line 35 to and through the 4-way valve 25, through the line 32 into the outlet end of the power cylinder 11. Hydraulic fluid forced out of the inlet end of the power cylinder 11 thus joins with the oil supplied by the main pump 20 to the outlet end of the cylinder 11 and thereby increases the volume of oil under pressure applied to the piston 12 of the cylinder 11 and moves the piston 12 and broaching slide 10 On their Return Stroke at a much greater speed than they are moved on their Power Stroke providing .a rapid return of the said broaching slide on its Return Stroke.

At the completion of the Return Stroke of the piston 12 and the broaching slide 10, the broaching slide 10 is in its UP or returned position Where it contacts a limit switch (not shown) activating a conventional electric control means (not shown) which permits the spring loaded 4-way control valve 25 to shift to its central or Neutral position ready for automatic bleeding of air from the main hydraulic system as hereinbefore described prior to the initiation of another Broaching Cycle.

The embodiment of the invention disclosed in FIGS. 4 and 4A is like and similar to the embodiment of the invention shown in FIGS. 1, 1A, 2 and 3 except that it is applied to a single slide push-down broaching machine, and the regenerative type rapid return of the broaching slide has been omitted. The hydraulic circuits for Neutral and the Power Stroke for the embodiment of the invention disclosed in FIGS. 4 and 4A are the same as employed in the embodiments of the invention disclosed in FIGS. 1, 1A, 2 and 3; therefore, the drawings and description thereof need not be repeated.

As viewed in FIG. 4, the 4-way control valve 250 has been shifted to the right to initiate the Return Stroke of the broaching slide by the movement of the piston 12 of the power cylinder 11 to its return or UP position. The said 4-way valve 250 is like and similar to the 4-way valve 25 of the embodiment of the invention disclosed in FIGS. 1, 1A, 2 and 3 except that its porting and flowthrough has been changed as shown in FIG. 4. During the said Return Stroke of the piston 12, hydraulic fluid under the required volume and pressure is supplied by the main pump 20 to the outlet end of the power cylinder 11 through the line 30, the 4way valve 250, and the line 32 which moves the said piston 12 of the power cylinder 11 and the broach slide through its Power Stroke to its Neutral position shown in FIG. 4, at which time the broaching slide 10 contacts a limit switch (not shown) which activates a conventional electric control which permits the spring loaded 4-way control valve 250 to shift to its Neutral position ready for the automatic bleeding of air from the main hydraulic system as hereinbefore described and the subsequent initiation of another Broaching Cycle. During the said Return Stroke, hydraulic fluid is forced out of the inlet end of the power cylinder and passes through the line 35, the 4-way valve 250, and the line 36 to and through the metering pump 22 to the tank T.

A pilot operated spring loaded closed check valve 380 may be employed in the embodiment of the invention disclosed in FIGS. 4 and 4A receiving its operating pressure to open the same through a pilot line 39 from the 4-way valve 250 when in its Return Stroke position shown in FIG. 4, which pilot operated check valve 380 provides a rapid rate of Return Stroke travel of the piston 12 of the power cylinder 11 and the broaching slide 10.

Alternatively, if a rapid return of the broaching or tool slide 10 is desired in the embodiment of the invention disclosed in FIGS. 4 and 4A, a suitable conventional servo mechanism (not shown) may be employed to increase or vary the rate of flow of hydraulic fluid through the positive displacement metering pump 22 during the Return Stroke of the piston 12 of the hydraulic cylinder 11. This would automatically increase or vary the rate at which hydraulic fluid is expelled from the said inlet end of the hydraulic power cylinder 11 during all or a portion of its Return Stroke thereby increasing or varying the rate of return of the piston 12 of the power cylinder 11 and the corresponding rate of return of the broaching or tool slide 10 on its Return Stroke. In the event this alternative was employed, a conventional spring loaded check valve 38 would be substituted for the pilot operated spring loaded check valve 380.

The invention has been disclosed and described herein in connection with the operation of the broaching slide of a pull-down and a push-down broaching machine to provide and assure smooth power stroke movement and advancement of the tool slide with respect to the work to substantially eliminate tool chatter, intermittent vibration and uncontrolled oscillation of a tool slide, which results in positive feed control and properly smooth finished tool cuts in the workpiece; however, it is obvious that the invention may be applied with advantageous effect in 6 other types of hydraulic cylinder powered machine tools and the like.

Although but a single embodiment of the invention and one modification thereof has been disclosed and described in detail, it is obvious that many changes may be made in the size, shape, arrangement and organization of the various elements of the invention, all without departing from the spirit and scope thereof as defined by the appended claims.

What is claimed is:

1. In a machine tool or the like including a reciprocable machine element and hydraulic power cylinder means having a piston connected to said machine element for moving the same sequentially from a Neutral position through its Power Stroke and its Return Stroke back to its Neutral position, the combination of a source of hydraulic fluid under pressure comprising a variable displacement main pump capable of delivering hydraulic fluid from a tank to said hydraulic cylinder at a pressure substantially greater than required to move the machine tool element on its Power Stroke and a positive displacement flow control metering pump capable of metering hydraulic fluid at a selected rate from the outlet end of said cylinder to said tank, and a motor driving said main pump and said flow control metering pump at a common rate of rotation, valve means including Neutral, Power Stroke and Return Stroke positions and means shifting the same to its Power Stroke position thereby directing hydraulic fluid under pressure from said tank to the inlet end of said hydraulic cylinder and directing hydraulic fluid expelled from the outlet end of said cylinder through said metering pump to said tank, and means for setting said metering pump to regulate the rate of discharge of hydraulic fluid from said cylinder and thereby regulating the feed rate of movement of said piston and said machine element during the Power Stroke thereof.

2. In a machine tool or the like including a reciprocable machine element and hydraulic power cylinder means having a piston connected to said machine element for moving the same sequentially from a Neutral position through its Power Stroke and its Return Stroke back to its Neutral position, the combination of a source of hydraulic fluid under pressure comprising a variable displacement main pump capable of delivering hydraulic fluid from a tank to said hydraulic cylinder at a pressure substantially greater than required to move the machine tool element on its Power Stroke and a positive displacement flow control metering pump capable of metering hydraulic fluid at a selected rate from the outlet end of said cylinder to said tank, and means driving said pumps, valve means including Neutral, Power Stroke and Return Stroke positions and means shifting the same to its Power Stroke position thereby directing hydraulic fluid under pressure from said tank to the inlet end of said hydraulic cylinder and directing hydraulic fluid expelled from the outlet end of said cylinder through said metering pump to said tank, and means for setting said metering pump to regulate the rate of discharge of hydraulic fluid from said cylinder and thereby regulating the feed rate of movement of said piston and said machine element during the Power Stroke thereof, said valve means includes means shifting the same upon the completion of said Power Stroke to its Return Stroke position whereupon hydraulic fluid is directed under pressure from said tank into the outlet end of the hydraulic cylinder and hydraulic fluid expelled from the inlet end of said cylinder is directed into said outlet end of said hydraulic cylinder together with said hydraulic fluid under pressure from said tank whereby to cause a rapid return of said piston on its Return Stroke, and said valve means causing said metering pump to be isolated from the Return Stroke hydraulic circuit during said Return Stroke for circulation of hydraulic fluid from the said tank through said metering pump and back to said tank.

3. In a machine tool or the like as claimed in claim 2 wherein said valve means includes means shifting the same upon the completion of said Return Stroke to its Neutral position whereat the piston is fully extended at the inlet end of said cylinder, whereupon hydraulic fluid under pressure pumped by said main pump from said tank is directed through a flow restricted by-pass line into the outlet end of said cylinder maintaining said piston and machine element in their extended position, said cylinder having an air bleed outlet therefrom located just below the lowermost piston ring when said piston is fully extended at the inlet end of said cylinder, and said air bleed being connected through said valve means to said positive displacement metering pump which withdraws hydraulic fluid entering said cylinder through said restricted by-pass line from the hydraulic system and returns said hydraulic fluid to said tank.

4. In a machine tool or the like as claimed in claim 2 wherein said valve means includes means shifting the same upon the completion of said Power Stroke to its Return Stroke position whereupon hydraulic fluid is directed under pressure from said tank to the outlet end of the hydraulic cylinder and hydraulic fluid expelled from the inlet end of said cylinder is directed to and through said metering pump to said tank.

5. In a machine tool or the like including a reciprocable machine element and hydraulic power cylinder means having a piston connected to said machine element for moving the same sequentially from a Neutral position through its Power Stroke and its Return Stroke back to its Neutral position, the combination of a source of hydraulic fluid under pressure comprising a variable displacement main pump capable of delivering hydraulic fluid from a tank to said hydraulic cylinder at a pressure substantially greater than required to move the machine tool element on its Power Stroke and a positive displacement flow control metering pump capable of metering hydraulic fluid at a selected rate from the outlet end of said cylinder to said tank, said means driving said pumps, valve means including Neutral, Power Stroke and Return Stroke positions and means shifting the same to its Power Stroke position thereby directing hydraulic fluid under pressure from said tank to the inlet end of said hydraulic cylinder and directing hydraulic fluid expelled from the outlet end of said cylinder through said metering pump to said tank, and means for setting said metering pump to regulate the rate of discharge of hydraulic fluid from said cylinder and thereby regulating the feed rate of movement of said piston and said machine element during the Power Stroke thereof, said valve means further including means shifting the same upon the completion of the said Power Stroke to its Return Stroke position whereupon hydraulic fluid is directed under pressure from said tank into the outlet end of the hydraulic cylinder and hydraulic fluid expelled from the inlet end of said cylinder is directed into said outlet end of said hydraulic cylinder together with said hydraulic fluid under pressure from said tank whereby to cause a rapid return of said piston on its Return Stroke, said valve means causing said metering pump to be inactive during said Return Stroke except for idle circulation of hydraulic fluid from the said tank through said metering pump and back to said tank, and said valve means also including means shifting the same upon the completion of said Return Stroke to its Neutral position whereat the piston is fully extended at the inlet end of said cylinder, whereupon hydraulic fluid under pressure pumped by said main pump from said tank is directed through a flow restricted by-pass line into the outlet end of said cylinder, said cylinder having an air bleed outlet therefrom located just below the lowermost piston ring when said piston is fully extended at 8 the inlet end of said cylinder, said air bleed being connected through said valve means to said positive displacement metering pump which withdraws said hydraulic fluid entering said cylinder through said restricted by-pass line from the hydraulic system and returns said hydraulic fluid to said tank.

6. In a machine tool or the like including a reciprocable machine element and hydraulic power cylinder means having a piston connected to said machine element for moving the same sequentially from a Neutral position through its Power Stroke and its Return Stroke back to its Neutral position the combination of a source of hydraulic fluid under pressure comprising a variable displacement main pump capable of delivering hydraulic fluid from a tank to said hydraulic cylinder at a pressure substantially greater than required to move the machine tool element on its Power Stroke and a positive displacement flow control metering pump capable of metering hydraulic fluid at a selected rate from the outlet end of said cylinder to said tank, and means driving said pumps, valve means including Neutral, Power Stroke and Return Stroke positions and means shifting the same to its Power Stroke position thereby directing hydraulic fluid under pressure from said tank to the inlet end of said hydraulic cylinder and directing hydraulic fluid expelled from the outlet end of said cylinder through said metering pump to said tank, means for setting said metering pump to regulate the rate of discharge of hydraulic fluid from said cylinder and thereby regulating the feed rate of movement of said piston and said machine element during the Power Stroke thereof, said valve means further including means shifting the same upon the completion of the said Power Stroke to its Return Stroke position whereupon hydraulic fluid is directed under pressure from said tank into the outlet end of the hydraulic cylinder and hydraulic fluid expelled from the inlet end of said cylinder is directed into said outlet end of said hydraulic cylinder together with said hydraulic fluid under pressure from said tank whereby to cause a rapid return of said piston on its Return Stroke, said valve means causing said metering pump to be inactive during said Return Stroke except for idle circulation of hydraulic fluid from the said tank through said metering pump and back to said tank, said valve means also including means shifting the same upon the completion of said Power Stroke to its Return Stroke position whereupon hydraulic fluid is directed under pressure from said tank to the outlet of the hydraulic cylinder and hydraulic fluid expelled from the inlet end of said cylinder is directed to and through said metering pump to said tank.

7. In a machine tool or the like as claimed in claim 6 wherein a by-pass return line to tank is provided ahead of the metering pump including therein a spring loaded closed pilot operated check valve receiving its operating pressure from said 4-way valve when in its Return position whereby to open said check valve thereby increasing the rate of movement of said cylinder and said machine element to their Neutral position.

References Cited UNITED STATES PATENTS 2,518,782 8/1950 Hipp 60-52 2,535,550 12/1950 Price 6052 2,768,500 10/1956 Tyler 60-52. 2,803,110 8/1957 Chittenden 60-52 2,929,212 3/1960 Lewis et a1. 6052 EDGAR W. GEOGHEGAN, Primary Examiner US. Cl. X.R. 

